7a.) Neuronal Control of Micturition

Question 1

Define micturition

Answer 1

Urination

Question 2

Describe 5 step basic process of micturition

Answer 2

1. Urine made in kidney
2. Urine stored in bladder
3. Sphincter muscles relax
4. Bladder muscle (detrusor) contracts
5. Bladder emptied via urethra and urine removed

Question 3

State 4 generic roles of the nervous sytem in relation to the lower urinary tract

Answer 3

• Provide sensations of bladder filling and pain
• Allow bladder to completely relax and accomodate increasing volumes of urine
• Iniate and maintain voiding so bladder empties completely with minimal residual volume
• To provide an integrated regulation of smooth muscle and skeletal muscle sphincters of urethra

Question 4

What centre in the brain is involved in the supraspinal regulation of micturition?

State it’s alternative name

Answer 4

Pontine micturition centre (PMC)

Also known as Barrington’s nucleus

Question 5

Where is the pontine micturition centre (Barrington’s nucleus) found?

Answer 5

Rostral pons

Question 6

State the two regions within the Pontine micturition centre (Barrington’s nucleus) and whether each has sympathetic or parasympathetic fibres

Answer 6

• L region: sympathetic fibres
• M region: parasympathetic

Question 7

State the generic role of the L region in the Pontine micturition centre (Barrington’s nucleus)

Answer 7

• Sympathetic fibres
• Storage of urine and therefore relaxation of bladder
• Contraction of sphincters
• Storage phase

Question 8

State the generic role of the M region of the Pontine micturition centre (Barrington’s nucleus)

Answer 8

• Parasympathetics
• Detrusor contraction and bladder emptying
• Inhibition of L centre and it’s sympathetics to allow bladder to contract and urethral sphincters to relax

Question 9

What 4 other brain centres does the Pontine micturition (Barrington’s nucleus) coordinate with?

Answer 9

• Medial frontal cortex
• Insular cortex
• Hypothalamus
• Periaqueductal gray (PAQ)

Question 10

What’s the role of the Periaqeuductal gray centre in micturition?

Answer 10

Acts as a relay station for ascending bladder information from spinal cord and incoming signals from higher brain areas

Question 11

State and describe the two phases of micturition/lower urinary tract function

Answer 11

• Storage/filling stage: bladder relaxes and accomodates increasing volumes of urine while urethral sphincters increase their tone to maintain continence
• Voiding phase: urethral sphincters relax and bladder contracts to allow urine to be expelled

Question 12

Is the extent of bladder contraction greater in men or women?

Answer 12

Men

Question 13

Why, in men, is the internal urethral sphincter more developed?

Answer 13

Prevent retrograde ejaculation

Question 14

How many layers of what type of muscle are found in the detrusor muscle of the bladder?

Answer 14

3 layers of smooth muscle

Question 15

Describe the structure of the internal urethral sphincter (sort of asking how it is formed)

Answer 15

• At lower tip of trigone bladder neck opens into posterior urethra (i.e. distal part of bladder neck) which extends over 2-3 cm
• Wall of posterior urethra has smooth muscle fibres of detrusor muscle interspersed with elastic tissue
• Forms interal urethral sphincter

Question 16

Describe the structure of the external urethral sphincter

Answer 16

Skeletal muscle- voluntary mainly slow twitch striated muscle fibres

Question 17

In females the interal urethral sphincter and external urethral sphincter are immediately adjacent; what structure lies between between internal and external urethral sphincter in males?

Answer 17

Prostrate

Question 18

What do we mean when we say bladder smooth muscle is ‘multiunit’?

Answer 18

There are no gap junctions between smooth muscle cells hence each smooth muscle must be stimulated by an axon hence there will be a 1:1 ratio between nerve endings and smooth muscle cells

Question 19

Sympathetic innervation to bladder and IUS arises from what part of spinal cord?

Answer 19

Interomediolateral cell column of 10th thoracic to 2nd lumbar vertebrate

Question 20

Parasympathetic innervation to the bladder arises from which part of the spinal cord?

Answer 20

Interomedial cell column from S2 to S4

Question 21

Somatic innervation, via motor neurones, to the EUS arises from which part of spinal cord?

Which nerve do these somatic motor neurones travel through/in?

Answer 21

S2 to S4

Travel via/in pudenal nerve

Question 22

Describe the shape of a normal cystometrogram

Answer 22

Question 23

What is bladder tone defined by?

Answer 23

Relationship between bladder volume and internal (intravesical) pressure

Question 24

Describe how you can measure bladder tone and produce a cystometrogram

Answer 24

• Insert catheter into urethra
• Empty bladder
• Record pressures in bladder while filling with 50ml incrememnts of water
• Record relationship between volume and pressure= cystometrogram - see blue curve

Question 25

Describe the shape of a normal cystocytogram

Answer 25

* Increase in volume from 0-50ml produces moderately steep rise in pressure * Additional volume increases up to 300ml produce almost no pressure increase- this high compliance is due to relaxation of detrusor muscle * At volumes higher than 400ml additional increases in volume produce steep rises in 'passive' pressure

Question 26

Bladder tone up to the point of triggering micturition is independent of extrinsic bladder innervation; true or false?

Answer 26

True

Question 27

At what bladder volume do we: * Sense the urge for voluntary bladder emptying * Sense fullness Why do we then not always need to go to the toilet as soon as we sense the urge?

Answer 27

* Urge to empty: 150ml * Fullness: 400-500ml Efferent impulses from brain, in a learned reflex, inhibit presynaptic parasympathetic neurones in sacral spinal cord to prevent detrusor muscle contraction until a socially acceptable opportunity to void arises. Voluntary contraction of EUS also helps.

Question 28

What two centres in brain inhibit micturition reflex?

Answer 28

* Cortical * Suprapontine

Question 29

Describe the storage phase of micturition

Answer 29

Sensory afferents: * **Stretch receptors**- detect strech of bladder and relay information, via pelvic sphlanchnic nerves, to sympathetic neurones in interomediolateral cell column of T10-L2 region * **Sympathetic fibres**- pre-ganglionics leave T10-T12 region and pass through lumbar splanchnic nerves to the superior hypogastric plexus where they give rise to right and left hypogastric nerves. These nerves lead to inferior hypogastric/pelvic plexus where pre-ganglionics synapse with post-ganglionics. Post ganglionics continue to bladder through distal portion of hypogastric nerve *(Note: distal portion also contains pre-ganglionic parasympathetic axons)* * **Somatic motor neurones:** L centre sends signal ???via inteneuron to motor neurone which originates in S2-S4 region???; motor neurone then travels via pudenal nerve to cause contraction of EUS

Question 30

What receptors are found in each of the following places in storage phase of micturition: * Detrusor muscle relaxation * Contraction IUS * Contraction EUs

Answer 30

* Detrusor relaxation: B3 * Contraction IUS: alpha1 * Contraction EUS: nAChR

Question 31

Which phase of micturition is the dominant phase?

Answer 31

Storage phase

Question 32

Describe the voiding phase of micturition

Answer 32

* **Afferent sensory fibres**: detect stretch in bladder and send signals to parsympathetic nucleus in interomediolateral S2-S4 region. At high levels of bladder stretch afferent sensory fibres send signal to M centre and activates it causing the M centre to inhibt L centre aand teh sympathetics. Activation of M centre also increases excitatory effect on parasympathetics pre-ganglionics leaving S2-S4 via pelvic splanchnic nerves. Pre-ganglionics synapse in with post-ganglionics in body and neck of bladder. Parasympathetics cause detrusor muscle contraction- urinate * Once reflex has started further impulses from stretch receptors cause continueing contraction of detrusor muscle * **Cortical centres** in brain inhbiit EUS muscle contraction * **Voluntary contraction of abdominal muscles** to further raise bladder pressure and aid voiding and complete emptying

Question 33

Micturition is activated when high pressure in bladder activates M centre which then excites parsympathetics and inhibits L centre and sympathetics; however, can this reflex also be activated by higher centres in brain if person desires to urinate?

Answer 33

Yes

Question 34

The majority of interneurons acting on parsympathetic nucleus in S2-S4 region (involved in voiding phase) are: a. ) Excitatory b. ) Inhibitory ...?

Answer 34

Most of interneurons acting on parasympathetic nucleus in S2-S4 region are inhibitory- this helps to make the storage phase the dominant phase alongside fact that voiding phase only activated by high pressures detected by stretch receptors

Question 35

During bladder filling neurones within M centre are trned off; true or false

Answer 35

True, only activated at critical levle of bladder distention OR if a higher centre in brain decides to activate

Question 36

Summarise the micturition reflex arc in words *(think of diagram from workbook)*

Answer 36

Question 37

What receptors, in the detrosuer muscle, do parasympathetics synase with to cause detrusor contraction?

Answer 37

M3

Question 38

Why are babies incontinent?

Answer 38

Babies only have voiding reflex as the neurones involved in storage reflex arc are unmyelinated at start of life

Question 39

Which spinal nerves are involved in urination and defeacation?

Answer 39

S2, S3, S4 | (S2, S3, S4 keeps shit off the floor)

Question 40

Describe and explain the consequences on micturition if someone has a lesion above T10-L12 (an upper motor neurone lesion)

Answer 40

* Transect inhibitory interneurones * No inhibition on parasympathetic nucleus * Activity of parasympathetics increases leading to overactive micturition reflex * Also interupted the sensory afferent travelling up spinal cord to T10-L2 so don't have +ve effect on sympathetics which cause relaxation of detrusor and contraction of IUS * Bladder fills with small amount of urine then empties In upper motor neurone lesion can also get situation where somatic motor neurone via pudendal nerve still intact hence causes contraction of EUS. So have increased detrusor contraciton but sphincter not open= detrusor sphincter dyssynergia which leads to hypertrophic bladder

Question 41

Describe and explain the consequences of a spinal lesion in S2-S4 or cauda equina region

Answer 41

* Lesion destroys parsympathetic neurone and incoming sensory inputs * Can't feel how full bladder is and have no way of telling bladder to contract * Have perpetual/overactive storage phase * Bladder increases in volume and stretches becomes big, loose and baggy * Bladder becomes overfull and start to leak urine- overflow incontinence

Question 42

See summary drawing in notes to revise fully

Question 44

State conditions under which sensory afferents send impulses to: * Sympathetics * Parasympathetics

Answer 44

* Sympathetics: low activity signals * Parasympathetics: high activity signals